Do villagers need to see the houses to it become valid?

Solution 1:

A villager must be able to detect the doors. This does not mean a direct line of sight, but rather being in a proximity (and probably waiting some seconds, because the game does not scan for villages all the time). Here are images from the wiki:

Yes, you will need to transport one villager within range of the doors and keep him there. I usually do this not with a minecart, but by simply building a corridor of blocks and pushing a guy through it.

Number of 32 doors is correct, villagers breed until number of adults is > nr_doors*0.35.

Solution 2:

Ok... What we might consider a house, and what a minecraft Villager considers a "house" are two very different things.

To answer your question, explicitly: Yes. If a villager is too far away from a "house", its AI will not consider it in its calculations when breeding.

To explain a bit further, a Villager's AI considers 3 things when identifying what a house is:

1. A door
2. Covered blocks (I.e. blocks that do not have direct sky access)
3. Uncovered blocks (I.e. blocks that do have direct sky access)

Walls and floor really have nothing to do with it. Therefore, using this logic, a "village" really does not need to take up much space at all.

This Video goes into more detail about everything to do with villagers, including the breeding mechanics, distances, and what villagers have to trade.